ASSESSMENT OF THE POWER AND FREQUENCY OF A BOOMER SEISMIC SYSTEM UNDER REAL-WORLD CONDITIONS

Acoustic equipment is frequently used by commercial and recreational fishers, scientists, and the military for site suitability surveys, seafloor mapping, research, and identification of economic and natural resources. Anthropogenic effects to marine mammals are regulated via the Marine Mammal Protection Act, Endangered Species Act, and the National Environmental Policy Act. A known acoustic output of these systems is of extreme importance, as more noise sources are being associated with detrimental effects to marine mammals and to ensure these systems comply with current regulations.

On September 23, 2006 we conducted an experiment designed to find the acoustic signature of a mid-frequency seismic system during realistic conditions. We used a CAT 200 Boomer (Applied Acoustics Engineering), a surface-towed, catamaran-mounted system with peak responses between 500 and 2000 Hz that is commonly used on the continental shelf because of its ability to produce high resolution for unconsolidated substrates.

Using the RV Auk, owned by the Gerry E. Studds Stellwagen Bank National Marine Sanctuary, we conducted a series of three tows. Tow 1 was vessel-only, designed to capture the acoustic signature of the vessel. Tow 2 was vessel and boomer, designed to capture both sounds to determine if the two could be separated during analysis. Tow 3 was boomer only, designed to capture the signature of the boomer using a stationary vessel with engines off and boomer firing.

Sounds were recorded via passive sound recorders (ARUs) (Cornell University). A series of low-frequency ARUs, recording up to 1 kHz, were previously deployed by SBNMS to record ambient noise, vessel traffic, and whale vocalizations. We deployed two additional high-frequency ARUs, recording up to 32 kHz. Locations were chosen shallower than 100 m to stay within the operational depth of the boomer.

Project goals include determining: the acoustic signature of the boomer, how far sound travels from the source, if recorded sounds are within the frequency range of vocalizing marine mammals, and developing an acoustical field map.

Data was analyzed with Raven software. Results show the boomer has a peak frequency of 1125 Hz and a maximum power of 109.4 dB. According to the Marine Mammal Protection Act, these values do not fall within a range deemed harmful to marine mammals.